Transmitting device, receiving device, transmitting method, and receiving method

ABSTRACT

In a transmitting device, each of the plurality of mapping candidates that make up the search space is configured from the same number of control channel elements as an aggregation level value, the control channel elements are obtained by dividing each physical resource block into a predetermined number, and the quantity of resource elements contained in each of the predetermined number of control channel elements in each physical resource block adopts at least two types of values. A search space setting unit ( 102 ) sets a search space of which the aggregation level value is 2 or more so that, between a plurality of mapping candidates, variation in the total quantity of resource elements contained in the control channel elements that make up the mapping candidates is as small as possible.

TECHNICAL FIELD

The present invention relates to a transmission apparatus, a receptionapparatus, a transmission method, and a reception method.

BACKGROUND ART

In recent years, accompanying the adoption of multimedia information incellular mobile communication systems, it has become common to transmitnot only speech data but also a large amount of data such as still imagedata and moving image data. Furthermore, studies are being activelyconducted in LTE-Advanced (Long Term Evolution Advanced) to realize hightransmission rates by utilizing broad radio bands, Multiple-InputMultiple-Output (MIMO) transmission technology, and interference controltechnology.

In addition, taking into consideration the introduction of variousdevices as radio communication terminals in M2M (machine to machine)communication and the like as well as an increase in the number ofmultiplexing target terminals due to MIMO transmission technology, thereis a concern regarding a shortage of resources in a mapping region for aPDCCH (Physical Downlink Control Channel) that is used for a controlsignal (that is, a “PDCCH region”). If a control signal (PDCCH) cannotbe mapped due to such a resource shortage, downlink data cannot beassigned to the terminals. Therefore, even if a resource region in whichdownlink data is to be mapped (i.e., a “PDSCH (Physical Downlink SharedChannel) region”) is available, the resource region may not be used,which causes a decrease in the system throughput.

As a method for solving such a resource shortage, a study is being madeof assigning, in a data region, control signals for terminals served bya radio base station apparatus (hereunder, abbreviated as “basestation”). A resource region in which control signals for terminalsserved by the base station are mapped is referred to as an EnhancedPDCCH (ePDCCH) region, a New-PDCCH (N-PDCCH) region, an X-PDCCH regionor the like. Mapping the control signal (i.e., ePDCCH) in a data regionas described above enables transmission power control on control signalstransmitted to a terminal near a cell edge or interference control forinterference by a control signal to another cell or interference fromanother cell to the cell provided by the base station.

Further, according to the LTE-Advanced system, to expand the coveragearea of each base station, relay technology is being studied in which aradio communication relay station apparatus (hereunder, abbreviated as“relay station”) is installed between a base station and radiocommunication terminal apparatuses (hereunder, abbreviated as“terminals”; may also be referred to as UE (user equipment)), andcommunication between the base station and terminals is performed viathe relay station. The use of relay technology allows a terminal thatcannot communicate with the base station directly to communicate withthe base station via the relay station. According to the relaytechnology that has been introduced in the LTE-Advanced system, controlsignals for relay are assigned in a data region. Since it is expectedthat the control signals for relay may be extended for use as controlsignals for terminals, a resource region in which control signals forrelay are mapped is also referred to as an “R-PDCCH.”

In the LTE (Long Term Evolution) system, a DL grant (also referred to as“DL assignment”), which indicates a downlink (DL) data assignment, and aUL grant, which indicates an uplink (UL) data assignment are transmittedthrough a PDCCH. The DL grant indicates to the terminal that a resourcein the subframe in which the DL grant is transmitted has been allocatedto the terminal. In an FDD system, the UL grant indicates that aresource in a target subframe that is the fourth subframe after thesubframe in which the UL grant is transmitted has been allocated to theterminal. In a TDD system, the UL grant indicates that the resource in atarget subframe that is the fourth or a subframe subsequent to thefourth subframe after the subframe in which the UL grant is transmittedhas been allocated to the terminal. In the TDD system, which one ofsubframes located after the subframe in which the UL grant istransmitted is to be taken as the target subframe to be assigned to theterminal depends on the time-division pattern of the uplink and downlink(hereinafter referred to as “UL/DL configuration pattern”). However, inevery UL/DL configuration pattern, the UL subframe is the fourthsubframe after the subframe in which the UL grant is transmitted or asubframe subsequent to the fourth subframe.

In the LTE-Advanced system, a region (R-PDCCH for relay station (relayPDCCH) region) in which channel control signals for relay stations aremapped is provided in the data region. Similarly to the PDCCH, a DLgrant and a UL grant are mapped to the R-PDCCH. In the R-PDCCH, the DLgrant is mapped in the first slot and the UL grant is mapped in thesecond slot (refer to Non-Patent Literature “hereunder abbreviated asNPL” 1). Mapping the DL grant only in the first slot reduces a delay indecoding the DL grant, and allows relay stations to prepare for ACK/NACKtransmission for DL data (transmitted in the fourth subframe followingreception of the DL grant in FDD). Thus, each relay station monitorschannel control signals transmitted using an R-PDCCH from a base stationwithin a resource region indicated by higher layer signaling from thebase station (i.e., a “search space”) and thereby finds the channelcontrol signal intended for the corresponding relay station.

In this case, the base station indicates the search space correspondingto the R-PDCCH to the relay station by higher layer signaling.

In the LTE and LTE-Advanced systems, one RB (resource block) has 12subcarriers in the frequency domain and has a width of 0.5 msec in thetime domain. A unit in which two RBs are combined in the time domain isreferred to as an RB pair (for example, see FIG. 1). That is, an RB pairhas 12 subcarriers in the frequency domain, and has a width of 1 msec inthe time domain. When an RB pair represents a group of 12 subcarriers onthe frequency axis, the RB pair may be referred to as simply “RB.” Inaddition, in a physical layer, an RB pair is also referred to as a PRBpair (physical RB pair). A resource element (RE) is a unit defined by asingle subcarrier and a single OFDM symbol (see FIG. 1).

The number of OFDM symbols per RB pair changes depending on the CP(cyclic prefix) length of the OFDM symbols. Further, the number of REsof a resource region in which an ePDCCH is mapped per RB pair differsdepending on the number of OFDM symbols and the number of REs used for areference signal (RS).

The number of OFDM symbols and a reference signal that can be used varyfor each subframe. Accordingly, in a subframe having a small number ofREs of a resource region in which an ePDCCH is mapped in a single RBpair, the ePDCCH reception quality decreases.

Further, the number of OFDM symbols used for a PDCCH is variable betweenone and four. Accordingly, in a case where a PDCCH region is notconfigured for an ePDCCH, the number of OFDM symbols that can be usedfor an ePDCCH decreases as the number of OFDM symbols of the PDCCHregion increases.

Further, the number of REs to be used for a reference signal differsaccording to the configuration of the reference signal as describedbelow (see FIG. 1).

(1) CRS (1, 2, 4 Tx):

A CRS (cell specific reference signal) is transmitted in all RBs.Although a CRS may also be transmitted in a data region in a subframeother than an MBSFN subframe, in an MBSFN subframe, a CRS is transmittedusing only the first two OFDM symbols. The position at which the CRS ismapped varies depending on the cell ID.

(2) DMRS (12 REs, 24 REs or 16 REs):

Utilization of a DMRS (demodulation reference signal) is dynamicallyindicated to the terminal from the base station by downlink assignmentcontrol information (DL assignment). The number of DMRSs that areconfigured can be varied for each user. The DMRS is transmitted in adata region.

(3) CSI-RS (2 REs or More):

A CSI-RS (channel state information reference signal) is transmitted inall RBs. The subframe to be transmitted depends on a predeterminedperiod.

A PDCCH and an R-PDCCH have four aggregation levels, i.e., levels 1, 2,4, and 8 (for example, see NPL 1). Levels 1, 2, 4, and 8 have six, six,two, and two “mapping candidates,” respectively. As used herein, theterm “mapping candidate” refers to a candidate region to which a controlsignal is to be mapped, and a search space is formed by a plurality ofmapping candidates. When a single aggregation level is configured for asingle terminal, a control signal is actually mapped to one of theplurality of mapping candidates of the aggregation level. FIG. 2illustrates an example of search spaces corresponding to an R-PDCCH. Theovals represent search spaces for each of the aggregation levels. Themultiple mapping candidates in each search space for each aggregationlevel are located in a consecutive manner on VRBs (virtual resourceblocks). The resource region candidates in the VRBs are mapped to PRBs(physical resource blocks) through higher layer signaling.

Studies are being conducted with respect to individually configuringsearch spaces corresponding to ePDCCHs for terminals. Further, withrespect to the design of ePDCCHs, part of the design of the R-PDCCHdescribed above can be used, and a design that is completely differentfrom the R-PDCCH design can also be adopted. In fact, studies are alsobeing conducted with regard to making the design of ePDCCHs and thedesign of R-PDCCHs different from each other.

As described above, a DL grant is mapped to the first slot and a ULgrant is mapped to the second slot in an R-PDCCH region. That is, aresource to which the DL grant is mapped and a resource to which the ULgrant is mapped are divided on the time axis. In contrast, for ePDCCHs,studies are being conducted with regard to dividing resources to whichDL grants are mapped and UL grants are mapped on the frequency axis(that is, subcarriers or PRB pairs), and with regard to dividing REswithin an RB pair into a plurality of groups.

CITATION LIST Non-Patent Literature NPL 1

-   3GPP TS 36.216 V10.1.0, “Physical layer for relaying operation”

SUMMARY OF INVENTION Technical Problem

For example, with respect to ePDCCHs, studies are being conducted withregard to dividing each PRB pair into a plurality of resources.Resources obtained by division within an RB pair are referred to as CCEs(control channel elements). Although the number of REs forming a singleCCE in a PDCCH is configured to a fixed number of 36 REs, the number ofREs forming a single CCE in this case varies depending on the divisionmethod. Possible division methods include a method that dividesresources on a per subcarrier basis and a method that divides resourcesby generating groups of resources (REs).

Depending on the number of REs in a PRB pair, the number of resourcedivisions in a PRB pair, or the division method, in some cases thenumbers of REs of the respective CCEs in a PRB pair are not uniform. Forexample, FIG. 3 illustrates an example in which a plurality of PRB pairs#A to #D are configured in the search spaces of ePDCCHs, in which eachPRB pair is divided into four CCEs in subcarrier units (for every threesubcarriers). In FIG. 3, the CCEs into which each PRB pair is dividedare referred to as CCE #(4N), CCE #(4N+1), CCE #(4N+2), and CCE #(4N+3),respectively (where N=0, 1, 2, 3). In FIG. 3, the first two OFDM symbolsare used for a PDCCH, and the remaining 12 OFDM symbols are used for anePDCCH. In addition, as shown in FIG. 3, among the OFDM symbols used foran ePDCCH, as REs to be used for a reference signal (CRS or DMRS), a CRSis located in an amount corresponding to two ports, and a DMRS islocated in an amount corresponding to four ports. Among the REs (144REs) forming the OFDM symbols used for an ePDCCH, the number of REs thatcan be used for an ePDCCH is 108 REs.

FIG. 4 shows the total number of REs forming the four CCEs in each PRBpair shown in FIG. 3. As shown in FIG. 4, CCE #(4N) includes 25 REs, CCE#(4N+1) includes 29 REs, CCE #(4N+2) includes 29 REs, and CCE #(4N+3)includes 25 REs. That is, there is an inequality in the number of REsforming each CCE in one PRB pair. Consequently, the ePDCCH receptioncharacteristics vary according to which CCE is used. In particular, whena different search space is configured for each terminal, if there is aterminal configured with a search space having a small number of REs anda terminal configured with a search space having a large number of REs,the ePDCCH reception characteristics vary between the terminals, whichis unfair to the terminal configured with a search space having asmaller number of REs.

An object of the present invention is to provide a transmissionapparatus, a reception apparatus, a transmission method, and a receptionmethod that can equalize resources available for ePDCCHs among terminalsand reduce an inequality in the reception characteristics of controlinformation.

Solution to Problem

A transmission apparatus according to an aspect of the present inventionincludes: a configuration section that configures a search space formedby a plurality of mapping candidates based on an aggregation levelvalue, each of the plurality of mapping candidates being formed by thesame number of control channel elements as the aggregation level value,the control channel elements being obtained by dividing each physicalresource block into a predetermined number of parts; and a transmissionsection that transmits control information mapped to one of theplurality of mapping candidates in the configured search space, inwhich: the numbers of resource elements included in the predeterminednumber of control channel elements in each of the physical resourceblocks take at least two kinds of values; and the configuration sectionconfigures the search space so that, in a search space for which theaggregation level value is at least two, among the plurality of mappingcandidates, a difference between total numbers of elements included incontrol channel elements forming the mapping candidates is minimized.

A reception apparatus according to an aspect of the present inventionincludes: a configuration section that configures a search space formedby a plurality of mapping candidates based on an aggregation levelvalue, each of the plurality of mapping candidates being formed by thesame number of control channel elements as the aggregation level value,the control channel elements being obtained by dividing each physicalresource block into a predetermined number of parts; and a receptionsection that receives control information mapped to one of the pluralityof mapping candidates forming the configured search space, in which: thenumbers of resource elements included in the predetermined number ofcontrol channel elements in each of the physical resource blocks take atleast two kinds of values; and the configuration section configures thesearch space so that, among the plurality of mapping candidates formingeach search space for which the aggregation level value is at least two,a difference between total numbers of elements included in controlchannel elements forming the mapping candidates is minimized.

A transmission method according to an aspect of the present inventionincludes: configuring a search space formed by a plurality of mappingcandidates based on an aggregation level value, each of the plurality ofmapping candidates being formed by the same control channel elements asthe aggregation level value, the control channel elements being obtainedby dividing each physical resource block into a predetermined number ofparts; transmitting control information mapped to one of the pluralityof mapping candidates in the configured search space; causing thenumbers of elements included in the predetermined number of controlchannel elements in each of the physical resource blocks to take atleast two kinds of values; and configuring the search space so that, ineach search space for which the aggregation level value is at least two,among the plurality of mapping candidates, a difference between totalnumbers of elements included in control channel elements forming themapping candidates is minimized.

A reception method according to an aspect of the present inventionincludes: configuring a search space formed by a plurality of mappingcandidates based on an aggregation level value, each of the plurality ofmapping candidates being formed by the same number of control channelelements as the aggregation level value, the control channel elementsbeing obtained by dividing each physical resource block into apredetermined number of parts; receiving control information mapped toone of the plurality of mapping candidates forming the configured searchspace; causing the numbers of elements included in the predeterminednumber of control channel elements in each of the physical resourceblocks to take at least two kinds of values; and configuring the searchspace so that, in each search space for which the aggregation levelvalue is at least two, among the plurality of mapping candidates, adifference between total numbers of elements included in control channelelements forming the mapping candidates is minimized.

Advantageous Effects of Invention

According to the present invention, an inequality in receptioncharacteristics of control information can be reduced by equalizingresources available for ePDCCHs among terminals.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram provided for describing a PRB pair;

FIG. 2 illustrates an example of search spaces corresponding toR-PDCCHs;

FIG. 3 illustrates an example of mapping of CCEs;

FIG. 4 shows the number of REs forming each CCE;

FIG. 5 is a block diagram illustrating main components of a base stationaccording to Embodiment 1 of the present invention;

FIG. 6 is a block diagram illustrating main components of a terminalaccording to Embodiment 1 of the present invention;

FIG. 7 is a block diagram illustrating the configuration of the basestation according to Embodiment 1 of the present invention;

FIG. 8 is a block diagram illustrating the configuration of the terminalaccording to Embodiment 1 of the present invention;

FIG. 9 illustrates a search space configuration example according toEmbodiment 1 of the present invention (configuration example 1);

FIG. 10 illustrates an example of localized allocation and distributedallocation of ePDCCHs;

FIG. 11 illustrates another search space configuration example accordingto Embodiment 1 of the present invention (configuration example 2);

FIG. 12 illustrates still another search space configuration exampleaccording to Embodiment 1 of the present invention (configurationexample 2);

FIGS. 13A and 13B are diagrams provided for describing a PRB pairaccording to Embodiment 1 of the present invention (configurationexample 3);

FIGS. 14A and 14B are diagrams provided for describing a PRB pairaccording to Embodiment 1 of the present invention (configurationexample 4);

FIGS. 15A and 15B show the numbers of REs forming CCEs according toEmbodiment 1 of the present invention (configuration example 4);

FIG. 16 illustrates a search space configuration example according toEmbodiment 1 of the present invention (configuration example 4);

FIG. 17 illustrates a search space configuration example according toEmbodiment 1 of the present invention (configuration example 4);

FIG. 18 illustrates a search space configuration example according toEmbodiment 2 of the present invention;

FIG. 19 illustrates a search space configuration example according toEmbodiment 2 of the present invention;

FIGS. 20A and 20B illustrate a mapping example of CCEs according toEmbodiment 3 of the present invention; and

FIG. 21 illustrates a search space configuration example according toEmbodiment 3 of the present invention.

DESCRIPTION OF EMBODIMENTS

Embodiments of the present invention are described in detail hereunderwith reference to the accompanying drawings. Throughout the embodiments,the same elements are assigned the same reference numerals, and aduplicate description of the elements is omitted

Embodiment 1 Communication System Overview

A communication system according to the present embodiment includes atransmission apparatus and a reception apparatus. In particular, thepresent embodiment is described by taking base station 100 as thetransmission apparatus and taking terminal 200 as the receptionapparatus. The communication system is, for example, an LTE-Advancedsystem. Base station 100 is, for example, a base station that supportsthe LTE-Advanced system, and terminal 200 is, for example, a terminalthat supports the LTE-Advanced system.

FIG. 5 is a block diagram illustrating main components of base station100 according to the present embodiment.

In base station 100, search space configuration section 102 configuressearch spaces formed by a plurality of “mapping candidates” based onaggregation level values. Each mapping candidate is formed of the samenumber of CCEs (control channel elements) as the aggregation levelvalue. The CCEs are obtained by dividing each PRB (physical channelresource block) pair into a predetermined number of parts. The number ofREs (resource elements) included in each of a predetermined number ofCCEs in each PRB pair takes at least two kinds of values. Search spaceconfiguration section 102 configures search spaces so that, in eachsearch space for which the aggregation level value is two or more, amonga plurality of mapping candidates, a difference between the totalnumbers of REs included in CCEs forming the mapping candidates isminimized.

Transmission section 106 transmits control information (DL assignmentand UL grant or the like) mapped to one mapping candidate among aplurality of mapping candidates in a search space configured by searchspace configuration section 102.

FIG. 6 is a block diagram illustrating main components of terminal 200according to the present embodiment.

Search space configuration section 205 in terminal 200 configures searchspaces formed by a plurality of “mapping candidates” based onaggregation level values. Each mapping candidate is formed of the samenumber of CCEs (control channel elements) as the aggregation levelvalue. The CCEs are obtained by dividing each PRB (physical channelresource block) pair into a predetermined number of parts. The number ofREs (resource elements) included in each of a predetermined number ofCCEs in each PRB pair takes at least two kinds of values. Search spaceconfiguration section 205 configures search spaces so that, in eachsearch space for which the aggregation level value is two or more, amonga plurality of mapping candidates, a difference between the totalnumbers of REs included in CCEs forming the mapping candidates isminimized.

Control signal reception section 206 extracts control information(control signal) mapped to one mapping candidate among a plurality ofmapping candidates forming a search space configured by search spaceconfiguration section 205. As a result, control information (DLassignment and UL grant or the like) transmitted from base station 100is received.

[Configuration of Base Station 100]

FIG. 7 is a block diagram illustrating the configuration of base station100 according to the present embodiment. As shown in FIG. 7, basestation 100 includes assignment information generation section 101,search space configuration section 102, error correction coding section103, modulation section 104, signal assignment section 105, transmissionsection 106, reception section 107, demodulation section 108, and errorcorrection decoding section 109.

In a case where there is a downlink data signal (DL data signal) to betransmitted and an uplink data signal (UL data signal) to be assigned toan uplink (UL), assignment information generation section 101 determinesresources (RB) to which assign the data signals are assigned, andgenerates assignment information (DL assignment and UL grant). The DLassignment includes information relating to assignment of the DL datasignal. The UL grant includes information relating to allocatedresources for the UL data signal to be transmitted from terminal 200.The DL assignment is outputted to signal assignment section 105, and theUL grant is outputted to reception section 107.

Based on aggregation level values, search space configuration section102 configures search spaces formed by a plurality of mapping candidatesfor each terminal 200 that uses an ePDCCH. Each “mapping candidate” isformed by the same number of CCEs as the aggregation level value. The“CCEs” are obtained by dividing each PRB pair into a predeterminednumber of parts.

For example, based on a value by which terminal 200 can be identifiedand a calculation formula that search space configuration section 102holds in advance, search space configuration section 102 determines asearch space (CCEs to be used in a search space) that is configured forthe relevant terminal 200. For example, a CRNTI (Cell Radio NetworkTemporary Identifier) that is indicated to terminal 200 from basestation 100 at the start of communication may be mentioned as a value bywhich terminal 200 can be identified. The aforementioned calculationformula is shared between base station 100 and terminal 200.

The aforementioned calculation formula is used to calculate CCEs formingsearch spaces to be configured for each terminal 200 so that aninequality does not arise with respect to the number of REs included inCCEs configured in the search spaces among the terminals 200. Morespecifically, for aggregation level 1 (number of CCEs forming a mappingcandidate: 1), search space configuration section 102 configures CCEs inwhich the numbers of REs are different from each other as a plurality ofmapping candidates to be configured for one terminal 200. Further, foraggregation levels 2, 4, and 8 (number of CCEs forming a mappingcandidate: 2, 4, and 8), among a plurality of mapping candidates to beconfigured for one terminal 200, search space configuration section 102configures CCEs in such a way that the CCEs include a CCE in which thenumber of REs is different from the others as at least one mappingcandidate. Note that processing to configure a search space performed bysearch space configuration section 102 is described in detail later.

Search space configuration section 102 outputs information relating to aconfigured search space (hereunder, may also be referred to as “searchspace information”) to signal assignment section 105. Search spaceconfiguration section 102 also outputs information relating to PRB pairsthat have been configured in a search space to error correction codingsection 103 as control information.

Error correction coding section 103 receives a transmission data signal(DL data signal) and control information received from search spaceconfiguration section 102 as input signals, performs error correctioncoding on the input signals, and outputs the processed signals tomodulation section 104.

Modulation section 104 modulates the signals received from errorcorrection coding section 103, and outputs the modulated data signal tosignal assignment section 105.

Signal assignment section 105 assigns the assignment information (DLassignment and UL grant) received from assignment information generationsection 101 to any CCE among CCEs (CCEs in mapping candidate units)indicated by search space information received from search spaceconfiguration section 102. Signal assignment section 105 also assignsthe data signal received from modulation section 104 to a downlinkresource corresponding to the assignment information (DL assignment)received from assignment information generation section 101.

A transmission signal is formed by assignment information and a datasignal being assigned to predetermined resources in this manner. Thethus-formed transmission signal is outputted to transmission section106.

Transmission section 106 executes radio transmission processing such asup-conversion on the input signal, and transmits the obtained signal toterminal 200 via an antenna.

Reception section 107 receives a signal transmitted from terminal 200via an antenna, and outputs the received signal to demodulation section108. More specifically, reception section 107 separates a signal thatcorresponds to a resource indicated by a UL grant received fromassignment information generation section 101 from the received signal,and executes reception processing such as down-conversion on theseparated signal and thereafter outputs the obtained signal todemodulation section 108.

Demodulation section 108 executes demodulation processing on the inputsignal, and outputs the obtained signal to error correction decodingsection 109.

Error correction decoding section 109 decodes the input signal to obtainthe received data signal from terminal 200.

[Configuration of Terminal 200]

FIG. 8 is a block diagram illustrating the configuration of terminal 200according to the present embodiment. As shown in FIG. 8, terminal 200includes reception section 201, signal separating section 202,demodulation section 203, error correction decoding section 204, searchspace configuration section 205, control signal reception section 206,error correction coding section 207, modulation section 208, signalassignment section 209, and transmission section 210.

Reception section 201 receives a signal transmitted from base station100 via an antenna, and after executing reception processing such asdown-conversion thereon, outputs the processed signal to signalseparating section 202.

Signal separating section 202 extracts a control signal relating toresource allocation from the reception signal received from receptionsection 201, and outputs the extracted signal to control signalreception section 206. Signal separating section 202 also extracts fromthe reception signal a signal corresponding to a data resource (that is,a DL data signal) indicated by the DL assignment output from controlsignal reception section 206, and outputs the extracted signal todemodulation section 203.

Demodulation section 203 demodulates the signal outputted from signalseparating section 202, and outputs the demodulated signal to errorcorrection decoding section 204.

Error correction decoding section 204 decodes the demodulated signaloutputted from demodulation section 203, and outputs the obtainedreceived data signal. In particular, error correction decoding section204 outputs “information relating to PRB pairs configured in a searchspace” transmitted as a control signal from base station 100, to searchspace configuration section 205.

Search space configuration section 205 identifies a search spaceconfigured for terminal 200 of search space configuration section 205that uses an ePDCCH. For example, first, based on information receivedfrom error correction decoding section 204, search space configurationsection 205 determines PRB pairs to configure in the search space. Next,based on a value (for example, a CRNTI) by which terminal 200 of searchspace configuration section 205 can be identified and a calculationformula that search space configuration section 205 holds in advance,search space configuration section 205 determines a search space (CCEsto be used for a search space) that has been configured for the relevantterminal 200. The aforementioned calculation formula is shared betweenbase station 100 and terminal 200. That is, in a similar manner tosearch space configuration section 102, search space configurationsection 205 configures a search space of terminal 200 thereof. Searchspace configuration section 205 outputs information relating to CCEsconfigured as the search space to control signal reception section 206.Note that search space configuration processing performed by searchspace configuration section 205 is described in detail later.

In a signal component received from signal separating section 202,control signal reception section 206 detects a control signal (DLassignment or UL grant) intended for terminal 200 of signal separatingsection 202 by performing blind decoding with respect to CCEs indicatedby information received from search space configuration section 205.That is, control signal reception section 206 receives a control signalmapped to one mapping candidate among a plurality of mapping candidatesforming a search space configured by search space configuration section205. Control signal reception section 206 outputs a detected DLassignment intended for terminal 200 of control signal reception section206 to signal separating section 202, and outputs a detected UL grantintended for terminal 200 thereof to signal assignment section 209.

When a transmission data signal (UL data signal) is inputted to errorcorrection coding section 207, error correction coding section 207performs error correction coding on the transmission data signal andoutputs the obtained signal to modulation section 208.

Modulation section 208 modulates the signal outputted from errorcorrection coding section 207, and outputs the modulated signal tosignal assignment section 209.

Signal assignment section 209 assigns the signal outputted frommodulation section 208 according to the UL grant received from controlsignal reception section 206, and outputs the obtained signal totransmission section 210.

Transmission section 210 executes transmission processing such asup-conversion on the input signal, and transmits the obtained signal.

[Operations of Base Station 100 and Terminal 200]

Operations of base station 100 and terminal 200 that have the aboveconfigurations will be described.

In the following description, for example, as shown in FIG. 3, PRB pairs#A to #D are configured as resources that can be used as ePDCCHs.Further, as shown in FIG. 3, each PRB pair is divided into four CCEs.More specifically, PRB pair #A includes CCE 0 to CCE 3, PRB pair #Bincludes CCE 4 to CCE 7, PRB pair #C includes CCE 8 to CCE 11, and PRBpair #D includes CCE 12 to CCE 15.

That is, in the following description, as shown in FIG. 4, the number ofREs included in each of the four CCEs in each PRB pair takes two kindsof values (25 REs and 29 REs). More specifically, the number of REsincluded in CCEs #(4N) (that is, CCEs 0, 4, 8, 12) and CCEs #(4N+3)(that is, CCEs 3, 7, 11, 15) is 25, and the number of REs included inCCEs #(4N+1) (that is, CCEs 1, 5, 9, 13) and CCEs #(4N+2) (that is, CCEs2, 6, 10, 14) is 29, where N is 0, 1, 2, or 3.

In addition, in the following description, it is assumed that the numberof mapping candidates for aggregation levels 1, 2, 4, and 8 is 4, 4, 4,and 2, respectively. That is, at aggregation level 1, four CCEs fromamong CCE 0 to CCE 15 are configured as mapping candidates,respectively. Further, at aggregation level 2, four mapping candidatesin which two CCEs are combined from among CCE 0 to CCE 15 areconfigured. Similarly, at aggregation level 4, four mapping candidatesin which four CCEs are combined from among CCE 0 to CCE 15 areconfigured, and at aggregation level 8, two mapping candidates in whicheight CCEs are combined from among CCE 0 to CCE 15 are configured.

Note that, when mapping candidates for each aggregation level areindicated one by one from base station 100 to terminal 200, the numberof bits required for indication increases. Therefore, a preset ofmapping candidates may be configured in advance. This preset correspondsto a VRB in as an R-PDCCH.

<Search Space Configuration Processing by Base Station 100>

In base station 100, search space configuration section 102 configuressearch spaces for each terminal 200 so that the numbers of REs includedin CCEs forming search spaces configured for each terminal 200 becomeequal between terminals 200. Hereunder, a method of configuring searchspaces for each aggregation level is described.

(Aggregation Level 1)

Search space configuration section 102 configures CCEs in which thenumbers of REs are different as a plurality of (in this case, four)mapping candidates. More specifically, as four mapping candidatesconfigured for one terminal 200, search space configuration section 102selects CCEs from among CCE 0 to CCE 15 in such a way that the CCEsinclude both CCEs in which the number of REs is 25 (CCE #(4N) and CCE#(4N+3)) and CCEs in which the number of REs is 29 (CCE #(4N+1) and CCE#(4N+2)).

For example, with respect to one terminal 200, search spaceconfiguration section 102 selects one CCE each from the four kinds ofCCEs, namely, CCE #(4N), CCE #(4N+1), CCE #(4N+2), and CCE #(4N+3),respectively, and configures the respective CCEs as four mappingcandidates that correspond to aggregation level 1. In this case, thefour mapping candidates are formed by 25 REs, 29 REs, 29 REs, and 25REs, respectively. That is, in the search space, CCEs in which thenumbers of REs are different from each other are included in CCEs thatform a plurality of (four) mapping candidates, respectively.

(Aggregation Level 2)

Search space configuration section 102 configures a search space so thatthe total numbers of REs included in the CCEs forming the mappingcandidates (that is, the total number of REs of two CCEs) become equalbetween the mapping candidates. In other words, search spaceconfiguration section 102 configures a search space so that, among aplurality of (four) mapping candidates forming the search space, adifference between the total numbers of REs included in the CCEs formingthe mapping candidates (that is, the total number of REs of two CCEs) isminimized. More specifically, search space configuration section 102selects two CCEs that include one set of the CCEs in which the number ofREs is 25 (CCE #(4N) and CCE #(4N+3)) and the CCEs in which the numberof REs is 29 (CCE #(4N+1) and CCE #(4N+2)) from among CCE 0 to CCE 15,and configures the selected CCEs as one mapping candidate.

For example, search space configuration section 102 configures CCE #(4N)(number of REs: 25) and CCE #(4N+2) (number of REs: 29) as a pair as asingle mapping candidate, and configures CCE #(4N+1) (number of REs: 29)and CCE #(4N+3) (number of REs: 25) as a pair as a single mappingcandidate. In this case, the number of REs of each of the four mappingcandidates is 54 (=29+25).

(Aggregation Level 4)

Similarly to the case of aggregation level 2, search space configurationsection 102 configures a search space so that among a plurality of(four) mapping candidates forming the search space, a difference betweenthe total numbers of REs included in the CCEs forming the mappingcandidates (that is, the total numbers of REs of four CCEs) isminimized. More specifically, search space configuration section 102selects four CCEs that include the same number of CCEs in which thenumber of REs is 25 (CCE #(4N) and CCE #(4N+3)) and CCEs in which thenumber of REs is 29 (CCE #(4N+1) and CCE #(4N+2)) from among CCE 0 toCCE 15, and configures the selected CCEs as one mapping candidate.

For example, search space configuration section 102 selects pairs offour CCEs that include one set of CCE #(4N) and CCE #(4N+3) in which thenumber of REs is 25 and CCE #(4N+1) and CCE #(4N+2) in which the numberof REs is 29 from among CCE 0 to CCE 15 and configures the selected CCEsas mapping candidates. That is, each of the mapping candidates includesone set of four kinds of CCEs obtained by dividing each PRB pair intofour parts. In this case, the mapping candidates are formed by 108(=25+29+29+25) REs.

(Aggregation Level 8)

Similarly to the case of aggregation levels 2 and 4, search spaceconfiguration section 102 configures a search space so that among aplurality of (two) mapping candidates forming the search space, adifference between the total numbers of REs included in the CCEs formingthe mapping candidates (that is, the total numbers of REs of eight CCEs)is minimized. More specifically, search space configuration section 102selects eight CCEs that include the same number of CCEs in which thenumber of REs is 25 (CCE #(4N) and CCE #(4N+3)) and CCEs in which thenumber of REs is 29 (CCE #(4N+1) and CCE #(4N+2)) from among CCE 0 toCCE 15, and configures the selected CCEs as one mapping candidate.

For example, search space configuration section 102 selects eight CCEsthat include two sets of CCE #(4N) and CCE #(4N+3) in which the numberof REs is 25 and CCE #(4N+1) and CCE #(4N+2) in which the number of REsis 29 from among CCE 0 to CCE 15 and configures the selected CCEs as amapping candidate. That is, each of the mapping candidates includes twosets of four kinds of CCEs obtained by dividing each PRB pair into fourparts. In this case, each of the mapping candidates is formed by 216(=(25+29+29+25)×2) REs.

By performing the above described processing, search space configurationsection 102 configures search spaces for terminal 200. Note that searchspace configuration section 102 performs the above described searchspace configuration for each terminal 200.

Here, as “an unequal configuration of search spaces (number of REs)between terminals 200”, for example, a case may be mentioned in which ina certain terminal 200 the mapping candidates are formed by only CCEs(CCE #(4N) and CCE #(4N+3)) in which the number of REs is 25, and inanother terminal 200 the mapping candidates are formed by only CCEs (CCE#(4N+1) and CCE #(4N+2)) in which the number of REs is 29. Whencomparing a case where an ePDCCH (control information) is allocatedusing only mapping candidates formed by only CCEs in which the number ofREs is 25 and a case where an ePDCCH (control information) is allocatedusing only mapping candidates formed by only CCEs in which the number ofREs is 29, although the channel quality between base station 100 andterminal 200 may be the same in both cases, an inequality arises in thereception quality at the respective terminals 200. In particular, ataggregation level 1, since the number of REs per mapping candidate issmall compared to the other aggregation levels, a situation should beavoided in which, among CCEs that include a different number of REs fromeach other, only CCEs having a small number of REs are configuredunequally in one terminal 200.

In this regard, according to the present embodiment, the number of REsthat can be used for an ePDCCH can be equalized among terminals 200 ataggregation levels 1, 2, 4, and 8. That is, at aggregation levels, adifference in the number of REs that can be used for an ePDCCH iseliminated between terminals 200. Therefore, base station 100 canequally configure the number of REs that can be used for an ePDCCH foreach terminal 200, and inequalities in the numbers of REs (inequality inthe reception quality) that can be used for an ePDCCH between terminals200 are moderated.

In addition, according to the present embodiment, at each of aggregationlevels 2, 4, and 8, since a difference in the number of REs between themapping candidates is minimized (in this case, the difference iseliminated), the number of REs that can be used for an ePDCCH can beequalized among the mapping candidates. That is, differences in thereception quality of terminals 200 that are attributable to the numbersof REs can be equalized among the mapping candidates. That is,inequalities in the numbers of REs (difference in the reception quality)are moderated by the selection of the mapping candidates to which thecontrol information is mapped.

Next, examples of configuring search spaces by performing the abovedescribed search space configuration processing is described. Hereunder,search space configuration examples 1 to 4 are described.

Configuration Example 1

FIG. 9 illustrates an example of configuring search spaces according toconfiguration example 1. The search spaces shown in FIG. 9 areconfigured for a single terminal 200, and search spaces different fromthe search spaces shown in FIG. 9 are configured for terminals 200 otherthan terminal 200 corresponding to FIG. 9.

As shown in FIG. 9, for aggregation level 1, CCE 0, CCE 5, CCE 10 andCCE 15 are configured as one mapping candidate. That is, for aggregationlevel 1, CCE #(4N), CCE #(4N+1), CCE #(4N+2) and CCE #(4N+3) are eachconfigured as a single mapping candidate.

Further, as shown in FIG. 9, for aggregation level 2, a pair of CCE 1and CCE 3, a pair of CCE 4 and CCE 14, a pair of CCE 9 and CCE 3, and apair of CCE 12 and CCE 14 are each configured as a single mappingcandidate. That is, for aggregation level 2, a pair of CCE #(4N) and CCE#(4N+2) or a pair of CCE #(4N+1) and CCE #(4N+3) is configured as onemapping candidate.

Further, as shown in FIG. 9, for aggregation level 4, a combination ofCCE 2, CCE 7, CCE 8 and CCE 13, a combination of CCE 1, CCE 6, CCE 11and CCE 12, a combination of CCE 0, CCE 1, CCE 2 and CCE 3, and acombination of CCE 8, CCE 9, CCE 10 and CCE 11 are each configured asone mapping candidate. That is, at aggregation level 4, a single mappingcandidate includes one set of CCE #(4N), CCE #(4N+1), CCE #(4N+2) andCCE #(4N+3).

In addition, as shown in FIG. 9, for aggregation level 8, a combinationof CCE 1, CCE 3, CCE 4, CCE 6, CCE 9, CCE 11, CCE 1 and CCE 14 and acombination of CCE 0, CCE 1, CCE 2, CCE 3, CCE 4, CCE 5, CCE 6 and CCE 7are each configured as one mapping candidate. That is, at aggregationlevel 8, a single mapping candidate includes two sets of CCE #(4N), CCE#(4N+1), CCE #(4N+2) and CCE #(4N+3).

Configuration Example 2

“Localized allocation” which allocates ePDCCHs collectively at positionsclose to each other on the frequency band, and “distributed allocation”which allocates ePDCCHs by distributing the ePDCCHs on the frequencyband are being studied as allocation methods for ePDCCHs (for example,see FIG. 10). Localized allocation is an allocation method for obtaininga frequency scheduling gain, and can be used to allocate ePDCCHs toresources that have favorable channel quality based on channel qualityinformation. Distributed allocation distributes ePDCCHs on the frequencyaxis, and can obtain a frequency diversity gain. In the LTE-Advancedsystem, both a search space for localized allocation and a search spacefor distributed allocation may be configured (for example, see FIG. 10).

Therefore, according to configuration example 2, a case is described inwhich a search space for localized allocation is configured foraggregation level 2 (aggregation level 1), search spaces for bothlocalized allocation and distributed allocation are configured foraggregation level 4, and a search space for distributed allocation isconfigured for aggregation level 8.

FIG. 11 illustrates an example of configuring search spaces according toconfiguration example 2. The search spaces shown in FIG. 11 areconfigured for a single terminal 200, and search spaces different fromthe search spaces shown in FIG. 11 are configured for terminals 200other than terminal 200 corresponding to FIG. 11. Note that since thecombinations of CCE #(4N), CCE #(4N+1), CCE #(4N+2) and CCE #(4N+3) ineach aggregation level are the same as in mapping example 1 (FIG. 9), adescription thereof is omitted here.

As shown in FIG. 11, for aggregation level 2 (aggregation level 1), fourmapping candidates are configured so as to be a localized allocation.For example, in FIG. 11, CCE 1 and CCE 3 forming one mapping candidateare both included in PRB pair #A shown in FIG. 3. Likewise, in FIG. 11,CCE 4 and CCE 6 forming one mapping candidate are both included in PRBpair #B shown in FIG. 3. The same situation also applies with respect tothe other mapping candidates. That is, one mapping candidate includesonly CCEs that are in the same PRB pair.

Further, as shown in FIG. 11, for aggregation level 4, two mappingcandidates are configured so as to be a distributed allocation, and theremaining two mapping candidates are configured so as to be a localizedallocation. For example, in FIG. 11, CCE 2, CCE 7, CCE 8 and CCE 13forming one mapping candidate are CCEs that are distributed between thePRB pair #A to PRB pair #D shown in FIG. 3. The situation is also thesame for the mapping candidate formed by CCE 1, CCE 6, CCE 11 and CCE 12shown in FIG. 11. On the other hand, in FIG. 11, CCE 0, CCE 1, CCE 2 andCCE 3 forming one mapping candidate are CCEs that are included in PRBpair #A shown in FIG. 3. The situation is also the same for the mappingcandidate formed by CCE 8, CCE 9, CCE 10 and CCE 11 shown in FIG. 11.That is, among the four mapping candidates, two mapping candidatesinclude one set of four kinds of CCEs (CCE #(4N), CCE #(4N+1), CCE#(4N+2) and CCE #(4N+3)) obtained by dividing the same PRB pair intofour parts, and the remaining two mapping candidates include one each ofthe above described four kinds of CCEs of different PRB pairs.

In addition, as shown in FIG. 11, for aggregation level 8, two mappingcandidates are configured so as to be a distributed allocation. Forexample, in FIG. 11, CCE 1, CCE 3, CCE 4, CCE 6, CCE 9, CCE 11, CCE 12and CCE 14 forming one mapping candidate are CCEs that are distributedbetween PRB pair #A to PRB pair #D shown in FIG. 3. The situation isalso the same for the mapping candidate formed by CCE 0, CCE 2, CCE 5,CCE 7, CCE 8, CCE 10, CCE 13 and CCE 15 shown in FIG. 11. That is, onemapping candidate includes CCEs that are in a plurality of PRB pairs.

Here, with respect to a localized allocation, even when base station 100selects a PRB pair for which the channel quality is favorable as aresource to be used for ePDCCHs, when there is a difference between thenumbers of REs in the CCEs in the relevant PRB pair, if a mappingcandidate formed by a CCE having a small number of REs is selected, thereception quality will deteriorate and it will be difficult to obtain afrequency scheduling gain.

In this respect, according to mapping example 2, similarly to mappingexample 1, the numbers of REs are equalized among the mapping candidates(a difference between the numbers of REs is minimized). Hence, forexample, with respect to aggregation levels 2 and 4, when base station100 selects a mapping candidate that corresponds to localizedallocation, regardless of which mapping candidate in a PRB pair forwhich the channel quality is favorable is selected, equivalent frequencyscheduling effects can be obtained.

A general solution with respect to the search space configuration shownin FIG. 11 is illustrated in FIG. 12. In FIG. 12, L represents a valuethat identifies terminal 200. For example, L is a CRNTI number thatidentifies terminal 200 that is allocated to the relevant terminal 200from base station 100. L is a value that is shared between base station100 and terminal 200. Further, in FIG. 12, a function (X mod 4)represents a remainder when X is divided by 4.

Thus, search space configuration section 102 configures different searchspaces for each terminal 200 by calculating CCEs based on the value of Lallocated to each terminal 200, respectively, and the calculationformulas shown in FIG. 12. As shown in FIG. 12, in the case ofaggregation level 1, combinations of four patterns exist depending onthe value of L. Further, for example, with respect to terminals 200 forwhich L=0, 4, 8, . . . (multiples of 4) are configured in FIG. 12, thesearch spaces that search space configuration section 102 configures arethe same as in FIG. 11.

Note that, in mapping example 2, CCEs are selected from the same PRBpair for localized allocation, and CCEs are selected from a plurality ofPRB pairs for distributed allocation. However, CCEs that are selectedfor localized allocation need not only be CCEs that are selected fromthe same PRB pair, and may be CCEs included in PRB pairs having PRBnumbers that are close to each other or CCEs included in PRB pairs inRBGs (RB groups) having RBG numbers that are close to each other.

Configuration Example 3

Configuration example 3 describes configuration with respect to asubframe in which CSI-RSs are mapped.

FIG. 13A illustrates an example in which, similarly to FIG. 3, one PRBpair is divided in subcarrier units into four CCEs (CCE #(4N), CCE#(4N+1), CCE #(4N+2), CCE #(4N+3)). However, in FIG. 13A, in addition toREs in which CRSs and DMRSs are mapped similarly to FIG. 3, REs in whichCSI-RSs are mapped can also not be used for ePDCCHs. That is, in FIG.13A, the number of REs that can be used for ePDCCHs is less than in FIG.3. More specifically, among the REs (144 REs) forming OFDM symbols to beused for ePDCCHs, the number of REs that can be used for ePDCCHs is 100REs.

As shown in FIG. 13B, the number of REs forming each CCE is 21 REs inCCE #(4N), 29 REs in CCE #(4N+1), 25 REs in CCE #(4N+2), and 25 REs inCCE #(4N+3). That is, compared to FIG. 4, in FIG. 13B, in CCE #(4N) andCCE #(4N+2) the number of REs used for ePDCCHs is decreased by 4 REswhich corresponds to the number of REs in which CSI-RSs are mapped.Further, with respect to the numbers of REs included in each of the fourCCEs in each PRB pair, although in FIG. 4 the numbers of REs take twokinds of values (25 REs and 29 REs), in FIG. 13B the numbers of REs takethree kinds of values (21 REs, 25 REs, and 29 REs), and hence aninequality in the numbers of REs forming the CCEs in one PRB pair iseven more noticeable.

In configuration example 3, in the case of aggregation level 2 (onemapping candidate: 2 CCEs), search space configuration section 102configures at least one mapping candidate that includes a pair of CCEsformed by a CCE with the largest number of REs and a CCE with thesmallest number of REs. For example, in FIG. 13B, search spaceconfiguration section 102 configures a pair formed by CCE #(4N) in whichthe number of REs is the smallest number of 21 REs and CCE #(4N+1) inwhich the number of REs is the largest number of 29 REs as one mappingcandidate.

Further, in the case of aggregation level 2 (one mapping candidate: 2CCEs), search space configuration section 102 configures at least onemapping candidate that includes CCEs in which the number of REs isdifferent from the pair that includes the CCE with the largest number ofREs and the CCE with the smallest number of REs. For example, in FIG.13B, search space configuration section 102 configures a pair formed byCCE #(4N+2) and CCE #(4N+3) in which the number of REs is 25, as onemapping candidate.

Thus, the mapping candidate including CCE #(4N) and CCE #(4N+1) isformed by 50 (=21+29) REs, and the mapping candidate including CCE#(4N+2) and CCE #(4N+3) is formed by 50 (=25+25) REs. That is, since adifference in the number of REs between mapping candidates is minimized(in this case, the difference is eliminated), the number of REs that canbe used for ePDCCHs can be equalized between mapping candidates. Thatis, differences in the reception quality at terminals 200 that areattributable to the numbers of REs can be equalized among the mappingcandidates.

Note that, in the case of aggregation levels 1, 4, and 8, the situationis the same as in configuration examples 1 or 2.

Configuration Example 4

According to mapping example 4, a case is described in which one REG(resource element group) is formed by two REs, and one CCE is formed byM*2 REs (M is an arbitrary natural number).

Further, in mapping example 4, REGs belonging to each CCE (four CCEs inthis case) are interleaved and mapped in PRB pairs.

For example, in FIG. 14A, among the REs that can be used for ePDCCHs,the REGs (2 REs) belonging to each CCE are disposed in ascending orderof the subcarrier numbers from the position of a smallest subcarriernumber (REG surrounded by a thick line in FIG. 14A) that is the smallestOFDM symbol number, and when REGs are disposed in the positions of allthe subcarrier numbers for the relevant OFDM symbol number, REGs arethen disposed in ascending order of the subcarrier numbers at the nextOFDM number. In FIG. 14A, REGs are disposed in the order of CCE 0 (CCE#(4N)), CCE 1 (CCE #(4N+1)), CCE 2 (CCE #(4N+2)) and CCE 3 (CCE#(4N+3)). The above described disposing of REGs is performed up to thelargest OFDM symbol number (in FIG. 14A, the 15th OFDM symbol). As aresult, as shown in FIG. 14B, the number of REs forming each of the CCEsis 28 REs in CCE #(4N), 28 REs in CCE #(4N+1), 26 REs in CCE #(4N+2),and 26 REs in CCE #(4N+3).

In addition, in FIG. 14A, since REGs are allocated in the order of CCE#(4N), CCE #(4N+1), CCE #(4N+2) and CCE #(4N+3), the relationship in thefollowing expression 1 is established with respect to the number of REsof each CCE.

[1]

Number of REs of CCE #(4N)≧number of REs of CCE #(4N+1)≧number of REs ofCCE #(4N+2)≧number of REs of CCE #(4N+3)  (Expression 1)

Search space configuration section 102 configures a search space so thata difference between the total numbers of REs among mapping candidatesis minimized. In particular, in the case of aggregation level 2 when thecondition of expression 1 is satisfied, search space configurationsection 102 configures two CCEs including one set of CCE #(4N) and CCE#(4N+3), and two CCEs including one set of CCE #(4N+1) and CCE #(4N+2)as mapping candidates. Thus, as shown in FIG. 14B, the number of REsforming the mapping candidate including CCE #(4N) and CCE #(4N+3) andthe number of REs forming the mapping candidate including CCE #(4N+1)and CCE #(4N+2) are both 54 (=28+26), and therefore match. That is,since a difference in the number of REs between the mapping candidatesis minimized (in this case, the difference is eliminated), the number ofREs that can be used for ePDCCHs can be equalized between the mappingcandidates. That is, differences in the reception quality at terminals200 that are attributable to the numbers of REs can be equalized amongthe mapping candidates.

Here, when the condition of expression 1 is satisfied, a difference inthe number of REs between CCEs is, at most, 2 REs. For example, when thenumber of REs of CCE #(4N+3) (that is, the CCE that is last in the orderof disposing the REGs) is taken as K, the numbers of REs of the CCEstake the values in cases 1 to 4 that are shown in FIG. 15A. As shown inFIG. 15A, the numbers of REs included in the respective four CCEs of onePRB pair take two kinds of values ((K+2) REs and K REs). For example,FIG. 14A corresponds to case 3 (K=26) shown in FIG. 15A.

Further, FIG. 15B shows total numbers of REs of mapping candidates (2CCEs) when, with respect to each case shown in FIG. 15A, CCE #(4N) andCCE #(4N+3) are taken as a pair, and CCE #(4N+1) and CCE #(4N+2) aretaken as a pair. As shown in FIG. 15B, it is found that a differencebetween the total numbers of REs between the above two kinds of mappingcandidates is, at most, 2 REs.

FIG. 16 illustrates an example of configuring search spaces according toconfiguration example 4. The search spaces shown in FIG. 16 areconfigured for a single terminal 200, and search spaces that aredifferent from the search spaces shown in FIG. 16 are configured forterminals 200 other than the terminal 200 corresponding to FIG. 16. Notethat, the cases for aggregation levels 1, 4, and 8 are the same as inconfiguration examples 1, 2, or 3, and hence a description thereof isomitted here.

As shown in FIG. 16, for aggregation level 2, four mapping candidatesare formed by any of a pair of CCE #(4N) and CCE #(4N+3) (CCE 4 and CCE7, CCE 8 and CCE 11) and a pair of CCE #(4N+1) and CCE #(4N+2) (CCE 1and CCE 2, CCE 13 and CCE 14).

A general solution for the search space configurations shown in FIG. 16is illustrated in FIG. 17. In FIG. 17, L represents a value thatidentifies terminal 200. For example, L is a CRNTI number thatidentifies the target terminal 200. L is a value that is shared betweenbase station 100 and terminal 200. Further, in FIG. 17, a function (Xmod 4) represents a remainder when X is divided by 4. Expressions 2, 3and 4 for calculating CCEs of a part of aggregation level 4 andaggregation level 8 shown in FIG. 17 are as follows.

[2]

CCE#X0=((CCE(L)mod 4)+((L mod 2)*2−1))mod 4

CCE#X1=((CCE(L+1)mod 4+4)+((L+1 mod 2)*2−1))mod 4+4

CCE#X2=((CCE(L+2)mod 4+8)+((L+2 mod 2)*2−1))mod 4+8

CCE#X3=((CCE(L+3)mod 4+12)+((L+3 mod 2)*2−1))mod 4+12   (Expression 2)

[3]

Same as aggregation level 2

CCE#1,CCE#2 If (CCE(L)mod 4)mod 4=0 or 3

CCE#0,CCE#3 If (CCE(L)mod 4)mod 4=1 or 2

CCE#5,CCE#6 If (CCE(L+1)mod 4+4)mod 4=0 or 3

CCE#4,CCE#7 If (CCE(L+1)mod 4+4)mod 4=1 or 2

CCE#9,CCE#10 If (CCE(L+2)mod 4+8)mod 4=0 or 3

CCE#8,CCE#11 If (CCE(L+2)mod 4+8)mod 4=1 or 2

CCE#13,CCE#14 If (CCE(L+3)mod 4+12)mod 4=0 or 3

CCE#12,CCE#15 If (CCE(L+3)mod 4+12)mod 4=1 or 2  (Expression 3)

[4]

CCEs not selected with Expression 3

CCE#0,CCE#3 If (CCE(L)mod 4)mod 4=0 or 3

CCE#1,CCE#2 If (CCE(L)mod 4)mod 4=1 or 2

CCE#4,CCE#7 If (CCE(L+1)mod 4+4)mod 4=0 or 3

CCE#5,CCE#6 If (CCE(L+1)mod 4+4)mod 4=1 or 2

CCE#8,CCE#11 If (CCE(L+2)mod 4+8)mod 4=0 or 3

CCE#9,CCE#10 If (CCE(L+2)mod 4+8)mod 4=1 or 2

CCE#12,CCE#15 If (CCE(L+3)mod 4+12)mod 4=0 or 3

CCE#13,CCE#14 If (CCE(L+3)mod 4+12)mod 4=1 or 2  (Expression 4)

Similarly to configuration example 2 (FIG. 12), search spaceconfiguration section 102 configures search spaces that differ for eachterminal 200 by calculating CCEs based on the values of L that areassigned to each terminal 200, and the calculation formulas shown inFIG. 17. For example, with respect to terminals 200 for which L=0, 4, 8,. . . (multiples of 4) are configured in FIG. 17, the search spaces thatsearch space configuration section 102 configures are the same as inFIG. 16.

As shown in FIG. 17, for aggregation level 2, pairs of CCEs that includeCCEs that are not used in aggregation level 1 are selected. Further, inFIG. 17, mapping candidates corresponding to the second row from the topof aggregation level 4 are formed by the same four CCEs as the fourmapping candidates of aggregation level 1.

In addition, mapping candidates (expression 2) corresponding to thefirst row from the top of aggregation level 4 are calculated based onthe mapping candidates corresponding to the second row from the top ofaggregation level 4.

Specifically, the CCEs of mapping candidates corresponding to the firstrow from the top of aggregation level 4 are calculated in the followingmanner based on the CCEs of the mapping candidates corresponding to thesecond row from the top of aggregation level 4. That is, if CCE #(4N) isadopted to form a mapping candidate corresponding to the aforementionedsecond row, then CCE #(4N+3) in the same PRB pair as the relevant CCE isadopted as a CCE of a mapping candidate corresponding to theaforementioned first row, and likewise, if CCE #(4N+3) is adopted in thesecond row, then CCE #(4N) in the same PRB pair as the relevant CCE isadopted in the first row, if CCE #(4N+1) is adopted in the second row,then CCE #(4N+2) in the same PRB pair as the relevant CCE is adopted inthe first row, and if CCE #(4N+2) is adopted in the second row, then CCE#(4N+1) in the same PRB pair as the relevant CCE is adopted in the firstrow. That is, the calculation formula illustrated in expression 2represents processing that shifts the CCEs of the mapping candidates ofthe aforementioned second row to calculate the CCEs of the mappingcandidates of the aforementioned first row. More specifically, ((L mod2)*2−1) in Expression (2) corresponds to the above described shiftprocessing. ((L mod 2)*2−1) is “+1” when L is an odd number, and is “−1”when L is an even number.

The foregoing describes search space configuration examples 1 to 4.

<Search Space Configuration Processing by Terminal 200>

In terminal 200, similarly to search space configuration section 102,search space configuration section 205 configures a configured searchspace for its own device. As a result, candidates as resources in whichcontrol information intended for the relevant terminal 200 is mapped aredetermined.

As described above, according to the present embodiment, base station100 (search space configuration section 102) and terminal 200 (searchspace configuration section 205) configure search spaces formed by aplurality of mapping candidates based on an aggregation level value.Each mapping candidate is formed by the same number of CCEs as theaggregation level value, and the CCEs are obtained by dividing each PRBpair into a predetermined number of parts. Further, the number of REsincluded in each of a predetermined number of CCEs in each PRB pairtakes at least two kinds of values. In this case, for each search spacefor which the aggregation level value is two or more, base station 100and terminal 200 configure the search space so that, among a pluralityof mapping candidates, a difference between the total numbers of REsincluded in CCEs forming the mapping candidates is minimized.

In addition, for a search space for which the aggregation level value isone, base station 100 and terminal 200 configure the relevant searchspace so that CCEs in which the numbers of REs are different from eachother are included in CCEs forming each of a plurality of mappingcandidates.

Thus, even if there is a difference in the number of REs included in theCCEs obtained by dividing each PRB pair, the resources that can be usedfor ePDCCHs can be equalized among terminals 200 and an inequality inthe reception characteristics of control information can be reduced.Further, at aggregation level two or more, resources that can be usedfor ePDCCHs can also be equalized among a plurality of mappingcandidates configured for one terminal 200, and an inequality in thereception characteristics of control information can be reduced.

Note that a value of L that is used in the present embodiment is notlimited to a CRNTI, and may be another identification number that isshared between base station 100 and terminal 200. Further, as the valueof L, an identification number may be used that is newly notified frombase station 100 to terminal 200. Further, a value obtained bymultiplying a plurality of identification numbers by each other may alsobe used as the value of L. For example, a value obtained by multiplyinga CRNTI number and a cell ID by each other may be used as the value ofL.

Embodiment 2

The present embodiment relates to a method of configuring a search spacefor a UL grant and a DL assignment. Note that a base station and aterminal according to the present embodiment share the same basicconfigurations as base station 100 and terminal 200 according toEmbodiment 1. Accordingly, a description will be provided referring backto FIGS. 7 and 8.

In the present embodiment, as one example, a case is described in whicheach PRB pair is divided into four CCEs.

According to the localized allocation of aggregation levels 1 and 2,since it is desired to transmit control signals (UL grant and DLassignment) using PRB pairs for which the channel quality is favorable,there is a demand to assign a UL grant and a DL assignment to the samePRB pair for which the channel quality is favorable.

Therefore, according to the present embodiment, at base station 100,search space configuration section 102 configures each of a search spacefor a UL grant and a search space for a DL assignment in the sameaggregation level. In addition, from the viewpoint of lowering theprobability of collision (blocking), search space configuration section102 configures a search space for a UL grant and a search space for a DLassignment, respectively, by means of mapping candidates that includeCCEs that are different from each other. Furthermore, at aggregationlevels 1 and 2 for which the value is less than the predetermined numberof divisions (in this case, four), search space configuration section102 configures a search space for a UL grant and a search space for a DLassignment, respectively, by means of mapping candidates including CCEsthat are different from each other within the same PRB pair.

There is also the possibility of different aggregation levels being usedas search spaces for a UL grant and a DL assignment.

In an ePDCCH, a UL grant and a DL assignment are indicated with DCI(downlink control information) that is control information for adownlink. There are a plurality of formats for the DCI. In particular, acase may be considered in which DCI format 0 is used for the UL grant,and among DCI formats that depend on the transmission mode, DCI format2, DCI format 2A, DCI format 2B, DCI format 2C or the like that supportMIMO transmission is used for the DL assignment. The format size (numberof bits) of DCI format 2, DCI format 2A, DCI format 2B, and DCI format2C is larger than the format size of DCI format 0. Hence, a search spacefor which an aggregation level value is larger than that of the UL grantis liable to be selected for the DL assignment. For example, in a casewhere DCI format 0 (number of bits: 43) is used for the UL grant, andDCI format 2C or DCI format 2B (number of bits: 58 or 57) is used forthe DL assignment, a search space of aggregation level 1 is configuredfor the UL grant and a search space of aggregation level 2 is configuredfor the DL assignment.

Therefore, according to the present embodiment, in base station 100,search space configuration section 102 configures a search space for aDL assignment of aggregation level 2 and a search space for a UL grantof aggregation level 1 (aggregation level next to the aggregation levelof the search space for the DL assignment) in the same PRB pair. At thistime, from the viewpoint of lowering the probability of collision(blocking), the respective search spaces that are configured in the samePRB pair are formed by CCEs that are different from each other in thePRB pair.

Search space configuration examples according to the present embodimentare described below.

(Aggregation Levels 1 and 2)

FIG. 18 illustrates an example of configuring search spaces ofaggregation levels 1 and 2 according to the present embodiment. In FIG.18, the relationships between the PRB pairs and CCEs are the same as inFIG. 3.

As shown in FIG. 18, in a search space for a DL assignment ofaggregation level 1, CCE 2, CCE 7, CCE 8 and CCE 13 are each configuredas a single mapping candidate. Further, as shown in FIG. 18, in a searchspace for a UL grant of aggregation level 1, CCE 0, CCE 5, CCE 10 andCCE 15 are each configured as a single mapping candidate.

As shown in FIG. 18, in a search space for a DL assignment ofaggregation level 2, a pair of CCE 1 and CCE 3, a pair of CCE 4 and CCE6, a pair of CCE 9 and CCE 11, and a pair of CCE 12 and CCE 14 are eachconfigured as a single mapping candidate. Further, as shown in FIG. 18,in a search space for a UL grant of aggregation level 2, a pair of CCE 0and CCE 2, a pair of CCE 5 and CCE 7, a pair of CCE 8 and CCE 10, and apair of CCE 13 and CCE 15 are each configured as a single mappingcandidate.

Attention will now be focused on the search spaces of aggregation level2 shown in FIG. 18 (portions surrounded by ovals formed by solid lines).

In FIG. 18, among the CCEs in PRB pair #A (CCE 0 to CCE 3) shown in FIG.3, while CCE 1 and CCE 3 are mapping candidates for the DL assignment,the remaining CCE 0 and CCE 2 are mapping candidates for the UL grant.Likewise, in FIG. 18, among the CCEs in PRB pair #B (CCE 4 to CCE 7)shown in FIG. 3, while CCE 4 and CCE 6 are mapping candidates for the DLassignment, the remaining CCE 5 and CCE 7 are mapping candidates for theUL grant. A similar situation applies with respect to PRB pairs #C and#D.

Note that a similar situation also applies with respect to the searchspaces of aggregation level 1. That is, in FIG. 18, among the CCEs inPRB pair #A (CCE 0 to CCE 3) shown in FIG. 3, while CCE 2 is a mappingcandidate for a DL assignment, CCE 0 that is another CCE in PRB pair #Ais a mapping candidate for a UL grant. Likewise, in FIG. 18, among theCCEs in PRB pair #B (CCE 4 to CCE 7) shown in FIG. 3, while CCE 7 is amapping candidate for a DL assignment, CCE 5 that is another CCE in PRBpair #B is a mapping candidate for a UL grant. A similar situationapplies with respect to PRB pairs #C and #D.

That is, in each of aggregation levels 1 and 2, a search space for a DLassignment and a search space for a UL grant are respectively formed bymapping candidates including mutually different CCEs in the same PRBpair. As a result, for example, with respect to aggregation level 2, ifit is determined that the channel quality of PRB pair #A is favorable,base station 100 can locate the DL assignment in CCE 1 and CCE 3 andlocate the UL grant in CCE 0 and CCE 2, to thereby transmit the UL grantand DL assignment simultaneously using PRB pair #A.

Next, attention will be focused on the search space for a UL grant ofaggregation level 1 and the search space for a DL assignment ofaggregation level 2 that are shown in FIG. 18 (portions surrounded byovals formed by broken lines).

In FIG. 18, among the CCEs in PRB pair #A (CCE 0 to CCE 3) shown in FIG.3, while CCE 1 and CCE 3 are mapping candidates for the DL assignment,CCE 0 that is another CCE in PRB pair #A is a mapping candidate for theUL grant. Likewise, in FIG. 18, among the CCEs in PRB pair #B (CCE 4 toCCE 7) shown in FIG. 3, while CCE 4 and CCE 6 are mapping candidates forthe DL assignment, CCE 5 that is another CCE in PRB pair #B is a mappingcandidate for the UL grant. A similar situation applies with respect toPRB pairs #C and #D.

That is, a search space for a DL assignment of aggregation level 2 and asearch space for a UL grant of aggregation level 1 are respectivelyformed by mapping candidates including mutually different CCEs in thesame PRB pair. As a result, for example, if it is determined that thechannel quality of PRB pair #A is favorable, base station 100 can mapthe DL assignment in CCE 1 and CCE 3 and map the UL grant in CCE 0, andthereby transmit the UL grant and DL assignment simultaneously using PRBpair #A.

Thus, search space configuration section 102 configures a search spacefor a UL grant and a search space for a DL assignment in each of theaggregation levels. Further, search space configuration section 102selects mutually different CCEs in the same PRB pair, and configures theCCEs as a mapping candidate of a search space for a UL grant and amapping candidate of a search space for a DL assignment, respectively.

Thus, base station 100 can map a UL grant and a DL assignment in mappingcandidates in the same PRB pair. That is, base station 100 can transmita UL grant and a DL assignment simultaneously using the same PRB pair.

In addition, search space configuration section 102 configures a searchspace for a UL grant of aggregation level 1 and a search space for a DLassignment of aggregation level 2 in the same PRB pair. Search spaceconfiguration section 102 also selects mutually different CCEs in thesame PRB pair, and configures the CCEs as a mapping candidate of asearch space for a UL grant and a mapping candidate of a search spacefor a DL assignment, respectively.

Thus, even when the aggregation levels of a UL grant and a DL assignmentare different in a localized allocation, base station 100 can map the ULgrant and the DL assignment in mapping candidates in the same PRB pair.

(Aggregation Levels 4 and 8)

FIG. 19 illustrates an example of configuring search spaces ofaggregation levels 4 and 8 according to the present embodiment. In FIG.19, the relationships between the PRB pairs and CCEs are the same as inFIG. 3.

As shown in FIG. 19, in a search space for a DL assignment ofaggregation level 4, a combination of CCE 0, CCE 5, CCE 10 and CCE 15, acombination of CCE 3, CCE 4, CCE 9 and CCE 14, a combination of CCE 4,CCE 5, CCE 6 and CCE 7, and a combination of CCE 12, CCE 13, CCE 14 andCCE 15 are each configured as a single mapping candidate. Further, asshown in FIG. 19, in a search space for a UL grant of aggregation level4, a combination of CCE 2, CCE 7, CCE 8 and CCE 13, a combination of CCE1, CCE 6, CCE 11 and CCE 12, a combination of CCE 0, CCE 1, CCE 2 andCCE 3, and a combination of CCE 8, CCE 9, CCE 10 and CCE 11 are eachconfigured as a single mapping candidate.

In addition, as shown in FIG. 19, in a search space for a DLassignment/UL grant of aggregation level 8, a combination of CCE 1, CCE3, CCE 4, CCE 6, CCE 9, CCE 11, CCE 12 and CCE 14 and a combination ofCCE 0, CCE 2, CCE 5, CCE 7, CCE 8, CCE 10, CCE 13 and CCE 15 are eachconfigured as a single mapping candidate.

As shown in FIG. 19, with respect to a distributed allocation also, toavoid collisions (blocking) between a DL assignment and a UL grant,search spaces formed by different CCEs are configured with respect to aDL assignment and a UL grant at the aggregation levels.

For example, with respect to the distributed allocations of aggregationlevel 4 shown in FIG. 19, while the CCEs that can be used in a searchspace for a DL assignment are (CCE 0, CCE 5, CCE 10, CCE 15) and (CCE 3,CCE 4, CCE 9, CCE 14), the CCEs that can be used in a search space for aUL grant are the remaining (CCE 2, CCE 7, CCE 8, CCE 13) and (CCE 1, CCE6, CCE 11, CCE 12). Further, with respect to aggregation level 8(distributed allocation only) shown in FIG. 19, although the searchspace for a DL assignment and the search space for a UL grant are thesame, the CCEs that constitute two mapping candidates are different fromeach other.

It is thereby possible for base station 100 to allocate a DL assignmentand a UL grant at the same time.

Further, between the search space for a UL grant of aggregation level 4and the search space of aggregation level 8 that are shown in FIG. 19,combinations also exist that enable base station 100 to simultaneouslyassign a DL assignment and a UL grant.

More specifically, a mapping candidate for a UL grant of aggregationlevel 4 (CCE 2, CCE 7, CCE 8, CCE 13) and a mapping candidate ofaggregation level 8 (CCE 1, CCE 3, CCE 4, CCE 6, CCE 9, CCE 11, CCE 12,CCE 14) that are shown in FIG. 19 are formed by mutually different CCEs.Hence, base station 100 can allocate these mapping candidates to a DLassignment and a UL grant simultaneously. The same also applies withrespect to a mapping candidate for a UL grant of aggregation level 4(CCE 1, CCE 6, CCE 11, CCE 12) and a mapping candidate of aggregationlevel 8 (CCE 0, CCE 2, CCE 5, CCE 7, CCE 8, CCE 10, CCE 13, CCE 15) thatare shown in FIG. 19.

Further, with respect to the localized allocations of aggregation level4 shown in FIG. 19, while the CCEs that can be used in a search spacefor a DL assignment are (CCE 4, CCE 5, CCE 6, CCE 7) and (CCE 12, CCE13, CCE 14, CCE 15), the CCEs that can be used in a search space for aUL grant are the remaining (CCE 0, CCE 1, CCE 2, CCE 3) and (CCE 8, CCE9, CCE 10, CCE 11). That is, although PRB pairs that are different fromeach other are mapped in the respective mapping candidates, adjacent PRBpairs are mapped in a mapping candidate for a DL assignment and amapping candidate for a UL grant. It is thereby possible for basestation 100 to simultaneously assign a DL assignment and a UL grantusing adjacent PRB pairs.

Note that, in terminal 200 also, search space configuration section 205performs similar processing to search space configuration section 102 ofbase station 100.

According to the present embodiment configured as described above, sincebase station 100 can transmit a UL grant and a DL assignmentsimultaneously using the same PRB pair in accordance with the channelquality of each PRB pair, a frequency scheduling gain can be obtained.Further, according to the present embodiment, similarly to Embodiment 1,even when there is an inequality in the number of REs included in CCEsthat are obtained by dividing within each PRB pair, resources that canbe used for ePDCCHs can be equalized among terminals 200 and aninequality in the reception characteristics of control information canbe decreased.

Note that DCI format 0 (for UL grants) and DCI format 1A (for DL grants)are the same size and can be subjected to blind decoding at the sametime. Therefore, in the present embodiment, base station 100 mayconfigure a search space for DCI format 4, DCI format 0, or DCI format1A as a search space for a UL grant, and configure a search space for aDCI format for a DL that is determined according to the transmissionmode as a search space for a DL grant. Since DCI format 1A is used in acase where communication cannot be performed using a DCI format with alarge number of bits such as a DCI format for a DL that is determinedaccording to the transmission mode and the like, the usage frequency ofDCI format 1A is low. Accordingly, a search space of DCI format 1A isconfigured to the same search space as a UL grant (DCI format 0), andthere is no significant problem even if a UL grant and a DL assignmentcan not be transmitted at the same time using the same PRB pair.Furthermore, whether or not DCI format 4 is used varies depending on thetransmission mode of the UL, and hence a configuration may be adopted inwhich terminal 200 performs blind decoding only in a case where DCIformat 4 is used.

In addition, in the present embodiment, if the number of REs of a CCE istoo small for transmitting a signal in DCI format for a DL, for example,a configuration is conceivable in which the search space (group ofmapping candidates) of aggregation level 1 for a DL assignment shown inFIG. 18 is not configured.

Embodiment 3

In Embodiments 1 and 2 a case was described in which each PRB pair isdivided into four CCEs. In contrast, the present embodiment describes acase in which each PRB pair is divided into three CCEs. Note that a basestation and a terminal according to the present embodiment share thesame basic configurations as base station 100 and terminal 200 accordingto Embodiment 1 and Embodiment 2. Accordingly, a description will beprovided referring back to FIGS. 7 and 8.

Similarly to Embodiments 1 and 2, search space configuration section 102of base station 100 configures search spaces so that the numbers of REsin CCEs forming search spaces that are configured for each terminal 200are equal among terminals 200. More specifically, search spaceconfiguration section 102 configures search spaces corresponding toaggregation levels 1, 2, 4, and 8 in the following manner.

In the following description, as one example, as shown in FIG. 20A, PRBpairs #A to #F are configured as resources that can be used for ePDCCHs.Further, as shown in FIG. 20A, each PRB pair is divided into three CCEs.More specifically, PRB pair #A includes CCE 0 to CCE 2, PRB pair #Bincludes CCE 3 to CCE 5, PRB pair #C includes CCE 6 to CCE 8, PRB pair#D includes CCE 9 to CCE 11, PRB pair #E includes CCE 12 to CCE 14, andPRB pair #F includes CCE 15 to CCE 17.

As shown in FIG. 20B, the numbers of REs included in the three CCEsinside each PRB pair take two kinds of values (37 REs and 34 REs),respectively. More specifically, the number of REs included in CCEs#(3N) (that is, CCEs 0, 3, 6, 9, 12, 15) and CCE #(3N+1) (that is, CCEs1, 4, 7, 10, 13, 16) is 37, and the number of REs included in CCE#(3N+2) (that is, CCEs 2, 5, 8, 11, 14, 17) is 34, where N is 0, 1, 2,3, 4 or 5.

In the following description, it is assumed that the number of mappingcandidates for aggregation levels 1, 2, 4, and 8 is 6, 6, 2, and 2,respectively. That is, at aggregation level 1, six CCEs from among CCE 0to CCE 17 are configured as mapping candidates, respectively. Further,at aggregation level 2, six mapping candidates in which two CCEs arecombined from among CCE 0 to CCE 17 are configured. Similarly, ataggregation level 4, two mapping candidates in which four CCEs arecombined from among CCE 0 to CCE 17 are configured, and at aggregationlevel 8, two mapping candidates in which eight CCEs are combined fromamong CCE 0 to CCE 17 are configured.

FIG. 21 illustrates a configuration example of search spaces accordingto the present embodiment. The search spaces shown in FIG. 21 areconfigured for a single terminal 200, and search spaces that aredifferent from the search spaces shown in FIG. 21 are configured forterminals 200 other than the relevant terminal 200.

(Aggregation Level 1)

Search space configuration section 102 configures CCEs in which thenumbers of REs are different as a plurality of (in this case, six)mapping candidates, respectively. More specifically, as six mappingcandidates that are configured for one terminal 200, search spaceconfiguration section 102 selects CCEs from among CCE 0 to CCE 17 so asto include both CCEs in which the number of REs is 37 (CCE #(3N) and CCE#(3N+1)) and a CCE in which the number of REs is 34 (CCE #(3N+2)).

For example, with respect to one terminal 200, search spaceconfiguration section 102 selects two CCEs each from the three kinds ofCCEs, namely, CCE #(3N), CCE #(3N+1), and CCE #(3N+2) and configures therespective CCEs as six mapping candidates that correspond to aggregationlevel 1. In FIG. 21, CCE 0 and CCE 9 (CCEs #(3N)), CCE 4 and CCE 13(CCEs #(3N+1)), and CCE 8 and CCE 17 (CCEs #(3N+2)) are configured assingle mapping candidates, respectively.

In this case, the six mapping candidates are formed by 37 REs, 37 REs,34 REs, 37 REs, 37 REs, and 34 REs, respectively. That is, in the searchspace, CCEs in which the numbers of REs are different from each otherare included in the CCEs that respectively constitute the plurality of(six) mapping candidates.

(Aggregation Level 2)

Search space configuration section 102 configures a search space so thatthe total numbers of REs included in the CCEs forming the mappingcandidates (that is, the total numbers of REs of two CCEs) are equalizedamong the mapping candidates. In other words, search space configurationsection 102 configures a search space so that, among a plurality of(six) mapping candidates forming the search space, a difference betweenthe total numbers of REs included in the CCEs forming the mappingcandidates (that is, the total numbers of REs of two CCEs) is minimized.More specifically, search space configuration section 102 selects twosets of a pair of CCE #(3N) and CCE #(3N+1), a pair of CCE #(3N+1) andCCE #(3N+2), and a pair of CCE #(3N+2) and CCE #(3N) from among CCE 0 toCCE 17, and configures the selected pairs as six mapping candidates.

In FIG. 21, a pair of CCE 6 and CCE 7 and a pair of CCE 15 and CCE 16(pairs of CCE #(3N) and CCE #(3N+1)), a pair of CCE 1 and CCE 2 and apair of CCE 10 and CCE 14 (pairs of CCE #(3N+1) and CCE #(3N+2)), and apair of CCE 5 and CCE 3 and a pair of CCE 14 and CCE 12 (pairs of CCE#(3N+2) and CCE #(3N)) are each configured as a single mappingcandidate.

The numbers of REs of the mapping candidates formed by the respectivepairs of three kinds that are described above are 74 (37+37) REs, 71(37+34) REs, and 71 (34+37) REs.

(Aggregation Level 4)

Similarly to the case of aggregation level 2, search space configurationsection 102 configures a search space so that among a plurality of (two)mapping candidates forming the search space, a difference between thetotal numbers of REs included in the CCEs forming the mapping candidates(that is, the total numbers of REs of four CCEs) is minimized. Morespecifically, search space configuration section 102 selects four CCEsfrom among CCE 0 to CCE 17 so as to include at least one of CCE #(3N),CCE #(3N+1), and CCE #(3N+2), and configures the selected CCEs as asingle mapping candidate.

For example, search space configuration section 102 configures any twomapping candidates from among: a mapping candidate (number of REs: 145)including two CCEs #(3N), one CCE #(3N+1), and one CCE #(3N+2); amapping candidate (number of REs: 145) including one CCE #(3N), two CCEs#(3N+1), and one CCE #(3N+2); and a mapping candidate (number of REs:142) including one CCE #(3N), one CCE #(3N+1), and two CCEs #(3N+2).

In FIG. 21, a combination of CCE 0, CCE 12, CCE 7 and CCE 2 (two CCEs#(3N), one CCE #(3N+1), one CCE #(3N+2)) and a combination of CCE 6, CCE1, CCE 13 and CCE 8 (one CCE #(3N), two CCEs #(3N+1), one CCE #(3N+2))are each configured as a single mapping candidate.

(Aggregation Level 8)

Similarly to the case of aggregation levels 2 and 4, search spaceconfiguration section 102 configures a search space so that among aplurality of (two) mapping candidates forming the search space, adifference between the total numbers of REs included in the CCEs formingthe mapping candidates (that is, the totals of the numbers of REs ofeight CCEs) is minimized. More specifically, search space configurationsection 102 selects eight CCEs from among CCE 0 to CCE 17 so as toinclude at least one of CCE #(3N), CCE #(3N+1), and CCE #(3N+2), andconfigures the selected CCEs as a single mapping candidate.

For example, search space configuration section 102 configures any twomapping candidates from among: a mapping candidate (number of REs: 290)including three CCEs #(3N), three CCEs #(3N+1), and two CCEs #(3N+2); amapping candidate (number of REs: 287) including three CCEs #(3N), twoCCEs #(3N+1), and three CCEs #(3N+2); and a mapping candidate (number ofREs: 287) including two CCEs #(3N), three CCEs #(3N+1), and three CCEs#(3N+2).

In FIG. 21, a combination of CCE 0, CCE 3, CCE 12, CCE 4, CCE 7, CCE 16,CCE 2 and CCE 11 (three CCEs #(3N), three CCEs #(3N+1), two CCEs#(3N+2)) and a combination of CCE 6, CCE 9, CCE 1, CCE 10, CCE 13, CCE5, CCE 8 and CCE 17 (two CCEs #(3N), three CCEs #(3N+1), three CCEs#(3N+2)) are each configured as a single mapping candidate.

By performing the above described processing, search space configurationsection 102 configures search spaces of terminal 200. Note that searchspace configuration section 102 performs the above described searchspace configuration for each terminal 200.

Thus, according to the present embodiment, similarly to Embodiments 1and 2, the number of REs that can be used for an ePDCCH can be equalizedamong terminals 200 at the aggregation levels 1, 2, 4, and 8. That is,at the aggregation levels, differences in the numbers of REs that can beused for ePDCCHs are eliminated between terminals 200. Therefore, basestation 100 can equitably configure the numbers of REs that can be usedfor ePDCCHs for each terminal 200, and inequalities in the numbers ofREs (difference in the reception quality) that can be used for an ePDCCHbetween terminals 200 are moderated.

In addition, according to the present embodiment, similarly toEmbodiments 1 and 2, at each of aggregation levels 2, 4, and 8, sincedifferences in the number of REs between the mapping candidates areminimized, the numbers of REs that can be used for ePDCCHs can beequalized among the mapping candidates. That is, differences in thereception quality of terminals 200 that are attributable to the numbersof REs can be equalized among the mapping candidates. In other words,inequalities in the numbers of REs (difference in the reception quality)are moderated by the selection of the mapping candidates in which tolocate the control information.

Furthermore, in FIG. 21, six mapping candidates are configured accordingto localized allocation in aggregation levels 1 and 2, and two mappingcandidates are configured according to distributed allocation inaggregation levels 4 and 8. Note that, in localized allocation onemapping candidate is formed by CCEs within the same PRB pair, and indistributed allocation one mapping candidate is formed by CCEs of aplurality of PRB pairs.

In FIG. 21, similarly to Embodiment 2 (see FIG. 18), in aggregationlevels 1 and 2 (portions surrounded by ovals formed by solid lines),mapping candidates are configured so that a UL grant and a DL assignmentare assigned to the same PRB pair (for example, a PRB pair withfavorable channel quality). That is, search space configuration section102 selects mutually different CCEs in the same PRB pair, and configuresthe selected CCEs as a mapping candidate for aggregation levels 1 and 2.It is thereby possible for base station 100 to locate a UL grant and aDL assignment for which the aggregation levels are different from eachother in mapping candidates in the same PRB pair. That is, base station100 can transmit a UL grant and a DL assignment simultaneously using thesame PRB pair.

Note that search space configuration section 205 of terminal 200performs similar operations as search space configuration section 102.

According to the present embodiment that is described above, even in acase where one PRB pair is divided into three CCEs, similarly toEmbodiments 1 and 2 (cases of dividing a PRB pair into four CCEs),resources that can be used for ePDCCHs can be equalized among terminals200, and an inequality in the reception characteristics of controlinformation can be reduced. Further, according to the presentembodiment, similarly to Embodiments 1 and 2, when the aggregation levelis 2 or more, resources that can be used for ePDCCHs can be equalizedamong a plurality of mapping candidates that are configured for oneterminal 200, and an inequality in the reception characteristics ofcontrol information can be reduced.

Note that, in the present embodiment, with respect to aggregation level2, mapping candidates are configured so as to include two sets of threekinds of pairs, namely, a pair of CCE #(3N) and CCE #(3N+1), a pair ofCCE #(3N+1) and CCE #(3N+2), and a pair of CCE #(3N+2) and CCE #(3N).However, according to the present embodiment, in aggregation level 2, itis also possible to use only the pair of CCE #(3N+1) and CCE #(3N+2) andthe pair of CCE #(3N+2) and CCE #(3N). In other words, a configurationmay also be adopted in which, in aggregation level 2, only CCE pairsformed by a CCE with the largest number of REs (CCE #(3N) or CCE#(3N+1)) and a CCE with the smallest number of REs (CCE #(3N+2)) areused. By adopting this configuration, the number of REs of all the pairsis 71, and thus the number of REs is the same among the mappingcandidates.

Further, in the present embodiment, as shown in FIG. 20B, when the sizeof only one CCE (CCE #(3N+2) in FIG. 20B) among three CCEs forming eachPRB pair is different, a configuration may also be adopted in which onlypairs that include the aforementioned CCE are configured as mappingcandidates of aggregation level 2. By adopting this configuration, it isalso possible to make the number of REs the same among the mappingcandidates. In the case illustrated in FIG. 20B, such a configurationmay be adopted by configuring only a pair of CCE #(3N+1) and CCE #(3N+2)and a pair of CCE #(3N+2) and CCE #(3N) as the mapping candidates ofaggregation level 2.

The foregoing describes the embodiments of the present invention.

Other Embodiments

[1] The embodiments have been described with the cases in which it isassumed that the search spaces of aggregation levels 1, 2, 4, and 8 have(4, 4, 4, 2) or (6, 6, 2, 2) “mapping candidates” respectively. However,the aggregation level values and the number of mapping candidates ateach aggregation level are not limited to these values.

[2] Although the embodiments have been described on the premise that PRBpairs are divided in the frequency axis direction (FDM: frequencydivision multiplexing), a direction in which PRB pairs are divided isnot limited thereto. That is, PRB pairs may also be divided in a codeaxis direction (CDM: code division multiplexing) or a time axisdirection (TDM: time division multiplexing).

[3] Although the embodiments have been described taking CCEs as divisionunits of PRB pairs, units obtained by further dividing CCEs may also betaken as division units of PRB pairs. In this case, each of theembodiments described above can be applied to the aforementioneddivision units that constitute each CCE. For example, when generatingCCEs, by generating one CCE by combining the aforementioned divisionunits in which the numbers of REs are different, variations in thenumbers of REs among CCEs that are generated can be suppressed.

[4] Although the embodiments have been described taking a case in whichthe present invention is formed by hardware as an example, it is alsopossible to realize the present invention by software in conjunctionwith hardware.

Each function block employed in the description of the above embodimentsmay typically be implemented as an LSI formed by an integrated circuit.These may be individual chips or partially or totally contained on asingle chip. The term “LSI” is adopted here, but this may also bereferred to as “IC,” “system LSI,” “super LSI,” or “ultra LSI” dependingon differing extents of integration.

Further, the method of circuit integration is not limited to an LSI, andimplementation using dedicated circuitry or general purpose processorsis also possible. After LSI manufacture, utilization of an FPGA (fieldprogrammable gate array), which can be programmed, or a reconfigurableprocessor that enables reconfiguration of connections or settings ofcircuit cells within an LSI is also possible.

Further, if integrated circuit technology emerges that replaces LSIs asa result of the advancement of semiconductor technology or a derivativeother technology, naturally it is also possible to carry out functionblock integration using such technology. Application of biotechnology orthe like is also possible.

A transmission apparatus according to this disclosure includes: aconfiguration section that configures a search space formed by aplurality of mapping candidates based on an aggregation level value,each of the plurality of mapping candidates being formed by the samenumber of control channel elements as the aggregation level value, thecontrol channel elements being obtained by dividing each physicalresource block into a predetermined number of parts; and a transmissionsection that transmits control information mapped to one of theplurality of mapping candidates in the configured search space, inwhich: the numbers of resource elements included in the predeterminednumber of control channel elements in each of the physical resourceblocks take at least two kinds of values; and the configuration sectionconfigures the search space so that, in a search space for which theaggregation level value is at least two, among the plurality of mappingcandidates, a difference between total numbers of elements included incontrol channel elements forming the mapping candidates is minimized.

In the transmission apparatus according to this disclosure, in a searchspace for which the aggregation level value is one, control channelelements having a different number of the resource elements from eachother are included in control channel elements that form the pluralityof mapping candidates.

In the transmission apparatus according to this disclosure, in a casewhere the aggregation level value is two and the predetermined number isfour, at least one of the plurality of mapping candidates is formed by apair of a control channel element having a largest number of theresource elements and a control channel element having a smallest numberof the resource elements.

In the transmission apparatus according to this disclosure, in a casewhere the aggregation level value is two and the predetermined number isfour, at least one of the plurality of mapping candidates is formed bycontrol channel elements having a different number of the resourceelements from the pair.

In the transmission apparatus according to this disclosure, in a casewhere the aggregation level value is four and the predetermined numberis four, each of the mapping candidates includes one set of the controlchannel elements of four kinds obtained by dividing one physicalresource block into four parts.

In the transmission apparatus according to this disclosure, at least oneof the mapping candidates includes one set of the four kinds of controlchannel elements of an identical physical resource block.

In the transmission apparatus according to this disclosure, at least oneof the mapping candidates includes one each of the four kinds of controlchannel elements of different physical resource blocks.

In the transmission apparatus according to this disclosure, in a casewhere the aggregation level value is eight and the predetermined numberis four, each of the mapping candidates includes two sets of the controlchannel elements of four kinds obtained by dividing one physicalresource block into four parts.

In the transmission apparatus according to this disclosure: the controlinformation is first information relating to a downlink or secondinformation relating to an uplink; the configuration section configures,for an identical aggregation level, a first search space for the firstinformation and a second search space for the second information; andthe first search space and the second search space are formed by themapping candidates formed of the control channel elements different fromeach other.

In the transmission apparatus according to this disclosure, at anaggregation level of a value smaller than the predetermined number, thefirst search space and the second search space are formed by the mappingcandidates formed of the control channel elements different from eachother within the identical physical resource block.

In the transmission apparatus according to this disclosure, the firstsearch space, and a third search space for the second information at anaggregation level adjacent to an aggregation level of the first searchspace are formed by the mapping candidates formed of the control channelelements different from each other within the identical physicalresource block.

A reception apparatus according to this disclosure includes: aconfiguration section that configures a search space formed by aplurality of mapping candidates based on an aggregation level value,each of the plurality of mapping candidates being formed by the samenumber of control channel elements as the aggregation level value, thecontrol channel elements being obtained by dividing each physicalresource block into a predetermined number of parts; and a receptionsection that receives control information mapped to one of the pluralityof mapping candidates forming the configured search space, in which: thenumbers of resource elements included in the predetermined number ofcontrol channel elements in each of the physical resource blocks take atleast two kinds of values; and the configuration section configures thesearch space so that, among the plurality of mapping candidates formingeach search space for which the aggregation level value is at least two,a difference between total numbers of elements included in controlchannel elements forming the mapping candidates is minimized.

A transmission method according to this disclosure includes: configuringa search space formed by a plurality of mapping candidates based on anaggregation level value, each of the plurality of mapping candidatesbeing formed by the same control channel elements as the aggregationlevel value, the control channel elements being obtained by dividingeach physical resource block into a predetermined number of parts;transmitting control information mapped to one of the plurality ofmapping candidates in the configured search space; causing the numbersof elements included in the predetermined number of control channelelements in each of the physical resource blocks to take at least twokinds of values; and configuring the search space so that, in eachsearch space for which the aggregation level value is at least two,among the plurality of mapping candidates, a difference between totalnumbers of elements included in control channel elements forming themapping candidates is minimized.

A reception method according to this disclosure includes: configuring asearch space formed by a plurality of mapping candidates based on anaggregation level value, each of the plurality of mapping candidatesbeing formed by the same number of control channel elements as theaggregation level value, the control channel elements being obtained bydividing each physical resource block into a predetermined number ofparts; receiving control information mapped to one of the plurality ofmapping candidates forming the configured search space; causing thenumbers of elements included in the predetermined number of controlchannel elements in each of the physical resource blocks to take atleast two kinds of values; and configuring the search space so that, ineach search space for which the aggregation level value is at least two,among the plurality of mapping candidates, a difference between totalnumbers of elements included in control channel elements forming themapping candidates is minimized.

The disclosure of the specification, drawings, and abstract included inJapanese Patent Application No. 2012-009267, filed on Jan. 19, 2012, isincorporated herein by reference in its entirety.

INDUSTRIAL APPLICABILITY

The present invention is useful in that, even in a case where there isan inequality with respect to the numbers of REs included in CCEsobtained by division within each PRB pair, the resources available forePDCCHs can be equalized among terminals and an inequality in receptioncharacteristics of control information can be reduced.

REFERENCE SIGNS LIST

-   -   100 Base station    -   200 Terminal    -   101 Assignment information generation section    -   102, 205 Search space configuration section    -   103, 207 Error correction coding section    -   104, 208 Modulation section    -   105, 209 Signal assignment section    -   106, 210 Transmission section    -   107, 201 Reception section    -   108, 203 Demodulation section    -   109, 204 Error correction decoding section    -   202 Signal separating section    -   206 Control signal reception section

1. A communication apparatus comprising: a receiver, which, inoperation, receives a control signal from a base station apparatus, thecontrol signal mapped to one of a plurality of search spaces configuredin an Enhanced Physical Downlink Control Channel (EPDCCH), and theEPDCCH defined in a data region of a subframe; a search spaceidentification circuitry, which, in operation, identifies the one searchspace on which the control signal is mapped among the plurality ofsearch spaces, each search space including a plurality of mappingcandidates for mapping the control signal, the EPDCCH including aplurality of resource block (RB) pairs, each RB pair divided into aplurality of control channel elements (CCEs), and each of the pluralityof mapping candidates having a same number of CCE(s) as an aggregationlevel, wherein when the aggregation level is one, at least one of theplurality of search spaces includes a first mapping candidate which is afirst CCE having a first number of resource elements (REs) that belongto a first RB pair and a second mapping candidate which is a second CCEhaving a second number of REs that belong to a second RB pair, whereinthe second number is different from the first number; and a decoder,which, in operation, decodes the identified search space and acquiresthe control signal that is mapped to one of the plurality of mappingcandidates included in the identified search space.
 2. The communicationapparatus according to claim 1, wherein the plurality of search spacesare a collection of search spaces configured for the communicationapparatus.
 3. The communication apparatus according to claim 1, whereineach of the plurality of CCEs is comprised of a plurality of divisionunits, the plurality of division units include a first division unit anda second division unit whose numbers of REs are different from eachother.
 4. The communication apparatus according to claim 1, wherein thecontrol signal indicates downlink assignment and uplink grant.
 5. Thecommunication apparatus according to claim 1, wherein the plurality ofCCEs are allocated on the EPDCCH by either of a localized allocation ora distributed allocation.
 6. The communication apparatus according toclaim 1, wherein each RB pair is divided into four CCEs, and the fourCCEs include the first CCE having the first number of REs and the secondCCE having the second number of REs.
 7. The communication apparatusaccording to claim 1, wherein when the aggregation level is two, atleast one of the plurality of mapping candidates includes the first CCEhaving the first number of REs and the second CCE having the secondnumber of REs, in each of the plurality of search spaces.
 8. Acommunication method comprising: receiving a control signal from a basestation apparatus, the control signal mapped to one of a plurality ofsearch spaces configured in an Enhanced Physical Downlink ControlChannel (EPDCCH), and the EPDCCH defined in a data region of a subframe;identifying the one search space on which the control signal is mappedamong the plurality of search spaces, each search space including aplurality of mapping candidates for mapping the control signal, theEPDCCH including a plurality of resource block (RB) pairs, each RB pairdivided into a plurality of control channel elements (CCEs), and each ofthe plurality of mapping candidates having a same number of CCE(s) as anaggregation level, wherein when the aggregation level is one, at leastone of the plurality of search spaces includes a first mapping candidatewhich is a first CCE having a first number of resource elements (REs)that belong to a first RB pair and a second mapping candidate which is asecond CCE having a second number of REs that belong to a second RBpair, wherein the second number is different from the first number; anddecoding the identified search space and acquiring the control signalthat is mapped to one of the plurality of mapping candidates included inthe identified search space.
 9. The communication method according toclaim 8, wherein the plurality of search spaces are a collection ofsearch spaces configured for the terminal apparatus.
 10. Thecommunication method according to claim 8, wherein each of the pluralityof CCEs is comprised of a plurality of division units, the plurality ofdivision units include a first division unit and a second division unitwhose numbers of REs are different from each other.
 11. Thecommunication method according to claim 8, wherein the control signalindicates downlink assignment and uplink grant.
 12. The communicationmethod according to claim 8, wherein the plurality of CCEs are allocatedon the EPDCCH by either of a localized allocation or a distributedallocation.
 13. The communication method according to claim 8, whereineach RB pair is divided into four CCEs, and the four CCEs include thefirst CCE having the first number of REs and the second CCE having thesecond number of REs.
 14. The communication method according to claim 8,wherein when the aggregation level is two, at least one of the pluralityof mapping candidates includes the first CCE having the first number ofREs and the second CCE having the second number of REs, in each of theplurality of search spaces.